Data networking involves hardware and software. On the software side, networking protocols are often designed for current or near-term hardware capabilities. Protocols often become widely adapted while at the same time networking hardware improves. Processors become more efficient and capable and communication mediums gain reliability and capacity. Over time, networking protocols designed in the past may become less suitable for the hardware that is available in the present. For example, a transport protocol might have mechanisms for ensuring reliability, responsiveness to congestion, and ordered delivery. Such mechanisms are often not well suited for new types of networks. Yet, to maintain continuous inter-network operability, older protocols are not practical to modify. There is a need for techniques that can translate advances in networking technology into improvements in the overall performance of possibly older protocols without having to change those protocols or their existing implementations.
Moreover, some capabilities of networking hardware have not been fully appreciated and realized. So-called smart NICs (Network Interface Cards), for example FPGA (Field Programmable Gate Array) NICs have become more common. These newer interfaces, like traditional NICs, provide physical and media connectivity. They also include additional processing capability, sometimes in the form of reconfigurable circuitry (e.g., FPGAs). These processing-augmented NICs may allow features of some protocols to be offloaded from the host's CPU (Central Processing Unit) to the NIC. Some smart NICs may even allow an entire transport protocol to be fully offloaded from a host's CPU to the smart NIC. However, this approach often requires significant host-side changes. For example, host-side software might need to be re-written to communicate directly with its NIC via a custom application programming interface (API) rather than via a standard transport protocol. In addition, most smart NICs with off-load functionality do not function as “bump in the line” (“in-line”) devices (i.e., devices that connect to a host's existing NIC). Thus, to upgrade a host from an ordinary NIC to a smart NIC, the host's ordinary NIC must be physically replaced with a new smart NIC. Large scale upgrades can be expensive and disruptive. There is a need for smart NICs that can be provided to hosts to improve network and host performance without necessarily requiring host-side software or hardware changes.
Moreover, as realized only by the inventors, the development of smart NICs has also made it possible to off-load application-level functionality to smart NICs. For example, a distributed application might have elements throughout a data center that need to exchange data. Some of those elements or their helper agents might be capable of being executed by a smart NIC. However, it has not been realized that application-level code (or other code) on in-line smart NICs might be capable of direct network communication without having to traverse their respective hosts and host network stacks.
Techniques related to the issues mentioned above are described below.